Middlesbrough 0 Chelsea 2: Fernando Torres flukes it for Rafa

Torres scored only his second goal of 2013 - and didn't know a thing about it.

They had to wait until the 51st minute before taking the lead, courtesy of a fluke from Fernando Torres, and it was not until the introduction of Eden Hazard that Chelsea were able to stamp their authority on a dogged but limited Boro side.

Victory sets up a mouth-watering quarter-final at Old Trafford on Sunday week but Sir Alex Ferguson and his Manchester United side will hardly be quaking in their boots.

Torres scored only his second goal of 2013 - and didn't know a thing about it.

Ramires' shot from the edge of the box, after being teed up by Yossi Benayoun, might have found the net without his team-mate's assistance but it skimmed off Torres' head and looped over Boro keeper Jason Steele.

It summed up Chelsea's performance at the Riverside last night. Not very pretty, but they did just enough.

Hazard gave the Blues a belated spark and after going close himself, he carved out a second goal for Victor Moses in the 73rd minute.

The Belgian played a delightful one-two with Oscar before squaring the ball to Moses, who could not miss.

But if Benitez wanted his players to provide demonstrative proof that they are right behind him, he will have been disappointed.

A listless Chelsea were fortunate to go in level at half-time against opponents with the worst form in the Championship this year.

In seasons gone by, Chelsea would have swept aside lower division outfits with the minimum of fuss but the swagger has gone out of their game.

And while Boro were not good enough to take advantage, for more than an hour Chelsea's performance did nothing to suggest Benitez can win over his army of critics in the dressing room and in the stands.

After a tentative start, it began to dawn on Boro that Chelsea were no great shakes these days. Tony Mowbray's side grew in confidence and should have been ahead at half-time.

Scott McDonald knows what it is like to find the net against European champions - he once scored the winner for Celtic against AC Milan.

But his radar was off when he headed Nicky Bailey's cross wide with the goal beckoning.

Petr Cech fumbled Mustapha Carayol's 20-yard shot in the 40th minute and John Terry had to hack the ball away before McDonald could pounce on the rebound.

Steele did not have a shot to save in the opening 45 minutes and still had not made a stop when Ramires' shot struck Torres to hand Chelsea a 51st-minute lead after Boro's defence failed to clear Oscar's cross.

Boro went into the game with seven defeats in nine games, but the side Benitez sent out was a massive gamble with eight changes from the Manchester City defeat on Sunday.

It was a night crying out for a Frank Lampard but the interim coach went for the untried, untested and unused.

Dutch teenager Nathan Ake was handed a full debut, and did well. Benayoun started his first Chelsea game since August 2011 while Paulo Ferreira made his season's bow.

Boro at least started better than they had the last time the teams met in the competition. That was in the 1997 Cup Final when Roberto Di Matteo scored after just 42 seconds, paving the way for a 2-0 Chelsea triumph.

The visitors did go close in the seventh minute following a forceful Ramires run through the midfield traffic. He fed Oscar whose angled ball into the box just eluded the stretching Moses.

The same pair combined again after 11 minutes with Oscar getting on the end of Moses' low cross only for Andre Bikey to block his goalbound shot.

That was effectively Chelsea's lot in the opening period but they improved after the restart and had chances to stretch their lead after the Spaniard's fortuitous goal.

Torres fired narrowly over the bar in their next attack despite a poor first touch and then sub Hazard curled a fine effort inches wide before Moses sealed victory with his 73rd minute goal.